In all my time swatching and doing comparisons, I've almost never found a pair of polishes to be an exact match.... Until now! Extra-special-huge thanks to reader Gladys for requesting these polishes for comparison!
Index and ring finger: OPI Pike's Peek-A-Boo Purple
Middle and pinkie finger: Orly Midnight Star
Now, despite the color match, these polishes do have a few formula differences. OPI Pike's Peek-A-Boo Purple is quite sheer and needs three coats. Orly Midnight Star is fairly opaque and is perfect in two coats. OPI Pike's Peek-A-Boo Purple is old formula OPI, which contains the lovely "Big Three" and is slightly thinner than your average polish. Orly Midnight Star is Big Three-Free, which means it is a little thick and goopy and takes quite a while to dry. Application issues with both polishes were minimal- just keep in mind what type of formula you are trying to apply and you will have no problems.
Finding an exact match of OPI Pike's Peek-A-Boo Purple is truly awesome. Originally released in 1996 as part of the OPI Rocky Mountain collection, OPI Pike's Peek-A-Boo Purple is extremely hard to find, and to the best of my knowledge was only released with that collection and never again produced. OPI Pike's Peek-A-Boo Purple is über-discontinued and quite ancient, you would have an extremely hard time trying to track down this "antique" polish. Orly Midnight Star just came out a few months ago and is readily available at numerous retailers and etailers - I've even seen the whole Orly Gems collection display at my local grocery stores and CVS Pharmacies!
So, to sum it all up: OPI Pike's Peek-A-Boo Purple = Orly Midnight Star.